A QR code (Quick Response code) is a two-dimensional matrix barcode that encodes data in a pattern of black and white modules arranged in a square grid. Originally invented by Denso Wave in 1994 for tracking automotive parts, QR codes have become ubiquitous for encoding URLs, contact information, payment details, and other data that can be quickly scanned by smartphone cameras.
QR codes and URL shortening are natural partners. A shorter URL produces a simpler QR code with fewer modules, which is easier to scan, can be printed at smaller sizes, and tolerates more damage or distortion. This is why URL shortening services frequently offer QR code generation as a companion feature. QR code technology books on Amazon cover the full range of applications.
The technical structure of a QR code includes finder patterns (the three large squares in the corners), alignment patterns, timing patterns, format information, version information, and the data area. Error correction codes allow the QR code to be read even when partially damaged or obscured.
QR codes support four encoding modes: numeric (most efficient for digits), alphanumeric (for uppercase letters and some symbols), byte (for arbitrary data), and kanji (for Japanese characters). The choice of mode affects the data capacity and the resulting code complexity. Barcode technology books on Amazon explain encoding details.